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{ 




BUREAU OF MINES 
INFORMATION CIRCULAR/1989 




Intrinsically Safe 5-V, 4-A 
Rechargeable Power 
Supply 

By John J. Sammarco 



UNITED STATES DEPARTMENT OF THE INTERIOR 



Mission: As the Nation's principal conservation 
agency, the Department of the Interior has respon- 
sibility for most of our nationally-owned public 
lands and natural and cultural resources. This 
includes fostering wise use of our land and water 
resources, protecting our fish and wildlife, pre- 
serving the environmental and cultural values of 
our national parks and historical places, and pro- 
viding for the enjoyment of life through outdoor 
recreation. The Department assesses our energy 
and mineral resources and works to assure that 
their development is in the best interests of all 
our people. The Department also promotes the 
goals of the Take Pride in America campaign by 
encouraging stewardship and citizen responsibil- 
ity forthe public lands and promoting citizen par- 
ticipation in their care. The Department also has 
a major responsibility for American Indian reser- 
vation communities and for people who live in 
Island Territories under U.S. Administration. 



C '^^ '- / 

Information Circular 9223 / z' - - 



i 



Intrinsically Safe 5-V, 4-A 
Rechargeable Power 
Supply 

By John J. Sammarco 



UNITED STATES DEPARTMENT OF THE INTERIOR 
Manuel Lujan, Jr., Secretary 

BUREAU OF MINES 
T S Ary, Director 



no.qaa3. 



Library of Congress Cataloging in Publication Data: 



Sammarco, John J. 

Intrinsically safe 5-V, 4-A rechargeable power supply. 

(Bureau of Mines information circular; 9223) 

Includes bibliographical references. 

Supt. of Docs, no.: I 28.27:9223. 

1. Electricity in mining-Safety Measures. 2. Storage batteries. I. Title. 
II. Series; Information circular (United States. Bureau of Mines); 9223. 

^TN295.U4 [TN343] 622 s [622'.8] 88-607917 



CONTENTS 

Page 

Abstract 1 

Introduction 2 

Acknowledgment 3 

Circuit description 3 

Main regulator circuit 3 

Input protection circuit 4 

Output protection circuit 5 

Circuit calibration 6 

Local regulation network 7 

Specifications 7 

Summciry 8 

Appendix A.-Intrinsic safety 9 

Appendix B. -Fabrication information 10 

Appendix C.-Battery charger 11 

ILLUSTRATIONS 

1. 5-V dc power supply 2 

2. 5-V dc power supply block diagram 3 

3. 5-V dc power supply schematic diagram 4 

4. Main regulator circuit 4 

5. Input protection circuit 5 

6. Output protection circuit 6 

7. Local regulation network 7 

C-1. Battery charging circuit schematic 11 

TABLE 

1. Resistor adjustments 6 



UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 


A 


ampere 


/zF 


microfarad 


"C 


degree Celsius 


mA 


milUampere 


h 


hour 


s 


second 


in 


inch 


V 


volt 


lb 


pound 


Vdc 


volt, direct current 


kohm 


kilohm 


W 


watt 



INTRINSICALLY SAFE 5-V, 4-A RECHARGEABLE POWER SUPPLY 

By John J. Sammarco^ 



ABSTRACT 

The U.S. Bureau of Mines has developed a regulated, intrinsically safe, rechargeable power supply 
for portable electronic equipment for underground use. The regulated output is ideal for microprocessor 
power requirements and is suited for operation in hazardous environments. Two rechargeable, sealed 
batteries are contained within the power supply. Provisions are made to use an external source of power 
if these batteries fail. Provisions are also made to charge these internal batteries when needed. The 
circuit is composed of three main circuits: the main regulator circuit, the input protection circuit, and 
the output protection circuit. The main regulator circuit provides remote voltage sensing, current 
sensing, fault monitoring, and internal thermal protection. The input protection circuit checks for 
excessive input current and low battery conditions. The output protection circuit contains two 
overvoltage detection devices. 

Schematics, a parts list, and a calibration procedure are provided in this report to enable readers to 
fabricate the power supply. 



^Electrical engineer, Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh, PA. 



INTRODUCTION 



NOTE -With the internal battery, the assembly is regarded as intrinsically safe. If the external 
source is used, the assembly and its associated equipment must remain in a nonhazardous area 
(fresh air). Battery charging must always be done in fresh air. Any alteration of the device as 
described in this report voids intrinsically safe operation and its subsequent approval. 



Bureau research results provide advancements in safety 
and increases in overall mining efficiency through im- 
proved technology. This research may result in devices 
that can readily be used by the mining industry, such as the 
intrinsically safe, rechargeable power supply (fig. 1) de- 
scribed in this report. 

The power supply was designed for portable, electronic 
equipment used in hazardous environments. For this 
application, the following criteria are noteworthy: The 
design must be intrinsically safe (see appendix A); circuit 
operation should be efficient to maximize battery life; and 
size and weight should be minimal to enhance portability. 



To meet these criteria, the design incorporates multiple 
and redundant protection circuits to ensure intrinsic safety. 
Integrated circuits incorporating multiple protection func- 
tions were used to minimize circuit count, thus reducing 
the size and increasing reliability. Components were se- 
lected to enable efficient operation to prolong battery life. 
A means for recharging the batteries exists. 

This report describes circuit operation, calibration, and 
gives parts lists and schematic diagrams for both the power 
supply and a battery charger. 





Figure 1.-5-V dc power supply (closed and open). 



ACKNOWLEDGMENT 



The author wishes to acknowledge John S. Gbruoski, 
electronics technician, Pittsburgh Research Center, for 
construction of the device and for assistamce during the 



testing and Mine Safety 
(MSHA) approval process. 



and Health Administration 



CIRCUIT DESCRIPTION 



A block diagram of the power supply is depicted in 
figure 2. The power supply circuit schematic is depicted in 
figure 3. This power supply circuit is composed of the 
main regulator circuit, the input protection circuit, and the 
output protection circuit. A description of operation for 
each of these circuits follows. 

MAIN REGULATOR CIRCUIT 

The functions of the main regulator circuit, shown in 
figure 4, are to convert the 8-V nominal battery voltage to 
a 5.0-V output, to provide protection from excessive cur- 
rent, and to provide protection from voltage fault condi- 
tions. The main regulator circuit achieves these functions 
with device Ul, a programmable linear voltage regulator. 
This part was selected because it contains provisions for 
remote voltage sensing, current sensing, fault monitoring, 
and internal thermal protection. Additionally, these 



features, incorporated on one chip, greatly reduce the need 
for external circuitry and simphfies design.'' 

Linear voltage regulation is achieved by Ul (pin 9) 
monitoring the output voltage at the remote sensing volt- 
age divider resistors (R6 and R7). The appropriate biasing 
is supplied to the series pass transistor Ql to maintain 
proper output voltage regulation. An increase in output 
voltage measured by Ul (pin 9) will cause the biasing of 
Ql to decrease. Ql becomes less conductive and the out- 
put voltage will decrease to the desired level of output 
voltage. Various output voltages can be obtained by sim- 
ply chcmging the remote sensing voltage. Potentiometer 
R7 enables changes in the remote sensing voltage divider 
network so that the output voltage can be adjusted. Once 



^Fritz, G. Versatile UC1834 Optimizes Linear Regulator Efficiency. 
Unitrode Corp., Application Note U-95, 1984, pp. 1-12. 



8-V dc 
battery 
source 



Switch 1 

ON 



EXT. 9 



Input 

protection 

network 



8 V dc 



d> 



Main 
regulator 

circuit 



5Vdc 



^ 



Output 

protection 

circuit 



External 
connector 



External * 
power 
source 
(User supplied) 




V 



Output, 
5-Vdc, 4A 



Switch 1 must be in the EXT. position to 
use battery charger or external power 



Figure 2.-5-V dc power supply block diagram. 



J2-2 



To battery 

sense CR1 CR2 CR3 



KEY 

rFI Indicates cofinections made to printed 

circuit board in tteat sink areo 



Heat sink, o\ Dl D2, D3 



+5Vdc + Vo 




Figure 3.-5-V dc power supply schematic diagram. 



®TP5 ®TP6 



/>^ 




Figure 4.-Main regulator circuit 

the voltage has been adjusted in a laboratory environment, 
no changes to this adjustment should be made while 
underground. 

Current sensing is used to limit the current into Ql to 
protect it from daunage cmd to regulate the maximum out- 
put current of the power supply. The input current is 
sensed by measuring the voltage across R25 vwth a current 
sensing amplifier internal to Ul. When current becomes 
excessive the base drive to Ql is decreased making Ql less 
conductive, which limits the output current. 



Output voltage fault detection provides protection for 
two separate voltage fault conditions-overvoltage and 
undervoltage of the output. The voltage fault detection 
will tolerate any voltage deviation within ±10% of the 
nominal output voltage. Any voltage outside this range 
will be treated as a fault. An overvoltage fault activates a 
crowbar circuit that switches on a shunt silicon-controlled 
rectifier (SCR). This effectively places a short circuit 
across the output causing a large increase in Ql's collector 
current. Before this current becomes excessive, the cur- 
rent sensing protection of Ul will activate to provide 
proper protection. 

A voltage fault delay line prevents transient voltage 
conditions from triggering the overvoltage and undervolt- 
age fault protection circuits. This delay is programmable 
by adding a capacitor from pin 11 to ground. The delay 
time is about 0.047 s for each microfarad of capacitance. 

Finally, a thermal shutdown circuit is incorporated in 
Ul. This circuit will shut down operation of Ul when the 
internal junction temperatures reach 165° C. This protects 
Ul from damage because of excessive power dissipation. 

INPUT PROTECTION CIRCUIT 

The input protection circuit of figure 5 serves two main 
functions: to provide protection against excessive input 
current and to detect low battery conditions. 

Excessive input current protection is needed to protect 
the main regulation circuit from damage because of over- 
heating and to limit the output current of the power supply 
to a safe level. The input current is limited to approxi- 
mately 4.0 A. This is achieved by sensing the current 
through R2 and turning Q2 off when excessive current is 



(To battery sense) 
-J2-2 




CRl CR2 CR3 
— <] — <1 — W— »To external power 

F1 



and battery 
charger 



TP3® 




5^l kn 



-^/4' 



02 ^ 
Figure 5.-lnput protection circuit. 



detected, thus opening the negative connection to the 
battery. The input current (I) is known by simply measur- 
ing the voltage across R2 (E) and applying Ohm's law 
where E = I * R. 

A voltage of 0.2 V will exist across the 0.05-ohm resis- 
tance of R2 when 4.0 A of input current is present. This 
0.2 V is amplified to about 6.64 V by the differential am- 
plifier circmt of U2. Next, this voltage is sent to the volt- 
age detection circuit of U3. When a 6.64-V or greater 
voltage is detected by U3, the gate of Q2 is biased to turn 
off Q2, thus disconnecting power from the battery to the 
power supply circuit. 

The circuit described for current protection is indepen- 
dent and redundant to the current protection circuitry of 
Ul described in the "Main Regulator Circuit" section. 
Overcurrent protection is also provided by fuse Fl. How- 
ever, a fuse is not recognized as a protection device when 
evaluating a circuit for intrinsic safety because the re- 
sponse time of the fuse is not adequate to prevent an igni- 
tion in a hazardous environment. 

The second function of the input protection circuit is to 
detect low battery conditions. Operation of the power 
supply during low battery voltages can deep discharge the 
batteries, which will shorten their useful hfe. Two 3.95- V, 
rechargeable, sealed batteries connected in series are used 
as the power source. This combination gives a total nom- 
inal working voltage of 7.9 V. When a low battery condi- 
tion of 6.5 V is detected by the circuitry of U3, the metad- 
lic oxide semiconductor field-effect transistor Q2 is turned 
off to disconnect the negative side of the batteries from the 
power supply circuitry. When the battery voltage increases 
to 6.6 V, U3 will turn Q2 on, thus restoring battery power 
to the power supply circuit. 



Device U3 is used in the overcurrent detection circuit 
and the low-battery-detection circuit. This is a dual volt- 
age detector device that operates from any supply voltage 
in the 1.6- to 16-V range and can monitor voltages greater 
than 1.3 V. The voltage detection trip points and hystere- 
sis levels are programmed by external resistor networks.^ 
U3 is a low-power complementary metallic oxide semicon- 
ductor (CMOS) device and typically requires only 3 mA 
for operation, thus minimizing the current drain on the 
batteries. 

Note that the input circuit also provides the ability to 
externally sense battery voltage, supply external power, and 
charge batteries. An external Une is designated for sensing 
battery voltage. This provides easy access for measure- 
ment of the battery voltage. A separate line is provided 
for external power operation or for battery charging. 
When power switch SWl is opened (off), the batteries can 
be bypassed so that external power can be supplied for 
operation. 

The maximum external voltage permitted through this 
line is 16 V. To charge the batteries, SWl must be closed 
and the battery charger must be connected. Information 
for the battery chcu^ger is given in appendix C. The bat- 
teries recharge at a constant potential source of 4.96 to 
5.10 V dc each, with a charging current of 1.2 A. 



CAUTION.-Do not attempt to recharge, replace, or 
connect batteries while in a hazardous environment. 
Also, do not attempt to use or connect external 
power while in a hazardous environment. 



OUTPUT PROTECTION CIRCUIT 

A separate and redundant overvoltage protection circuit 
is present at the output as shown in figure 6. Shunt SCR 
circuits will be activated when an overvoltage condition 
exists. Two identical shunts are provided. This redundan- 
cy provides protection if a failure would occur in one of 
the shunts. The level at which the SCR's will turn on is 
determined by resistive divider networks. These trip levels 
can be adjusted. Potentiometer R9 adjusts the level for 
SCR D2 and potentiometer Rll adjusts the level for SCR 
D3. 

When a shunt SCR turns on, it effectively makes a 
short-circuit connection across the output of the power 
supply. During short-circuit output conditions, a large 
short-circuit current will flow through the power supply. 
The power supply will shut down when this current ex- 
ceeds the levels set by the current protection devices. 
Once £m SCR has tripped, it must be reset by momentarily 
disconnecting battery supply voltage by toggling power 
supply switch SWl to the off position. 



^Maxim Integrated Products Inc. (Sunnyvale, CA). Maxim Power 
Supply Circuits Data Book. 1986, pp. 113-123. 



(«)TP1 



+ 5 Vdc ^ w 




OUT 



B'^ ^ 



'OUT 



®TP2 
Figure 6.-0utput protection circuit. 



CIRCUIT CALIBRATION 



Once circuit construction is completed, it is necessary 
to adjust and calibrate the circuit to insure proper opera- 
tion. All adjustments, after setting, should remain fixed. 
No adjustments should be made whUe undergroimd. First 
the nominal output voltage is adjusted, then the output 
overvoltage protection trip points are set. 

Before the nominal output voltage can be set, it is nec- 
essary to temporairily prevent the overvoltage protection 
circuits of D2 and D3 from tripping. If these trip points 
are below the nominal output voltage, D2 and/or D3 will 
turn on and prevent the adjustment of the output voltage. 
To set the trip points above nominal, adjust R9 and Rll 
fully clockwise. Next, with battery voltage appUed to the 
circuit, connect a load resistance of 2 ohms (15-W mini- 
mum) to the output and adjust R7 until 5 V dc is mea- 
sured from test points TPl to TP2. 

To set the output overvoltage protection trip points, 
disconnect the batteries from the circuit and remove Ul 
and the 2-ohm output load. Connect a variable power 
supply capable of providing at least 6 V at 1 A to the out- 
put of the power supply circuit. This connection should 
include a 2-ohm, 15-W current limiting resistor in series 



from the positive terminal of the variable power supply to 
the positive output terminal of the intrinsically safe power 
supply. Set the voltage of the variable power supply to 5.3 
V dc. Turn R9 counterclockwise until SCR D2 turns on 
and draws significant current from the variable power sup- 
ply. Next, increase the voltage to 5.35 V dc and then turn 
off the variable power supply to reset D2. Turn the power 
supply on and adjust Rll until D3 turns on. Turn off the 
variable power supply and disconnect it from the output. 
Replace Ul. This completes the calibration. Table 1 lists 
the resistors used in the calibration sequences and their 
adjustment ranges. 

Table 1. -Resistor adjustments 

Potentiometer Adjustment Range, V dc 

R7 Allows output voltage to be 3.2- 5.5 

adjusted. 

R9 Varies trip point of rectifier D2 3.2-12.0 

for overvoltage protection. 

Rll Varies trip point of rectifier D3 3.2-12.0 

for overvoltage protection. 



LOCAL REGULATION NETWORK 



Although the output of the power supply is limited to a 
nominal output of 5 V, it can be used in a variety of appli- 
cations requiring multiple voltages by using a local regula- 
tion network (note that any additional circuits connected 
to the power supply must also be evaluated for intrinsic 
safety). For example, figure 7 depicts a system requiring 
multiple voltages. By using the 5-V supply as the primary 
voltage, the other voltages can be derived at each circuit 
board as needed. For instance, ±15 V can be derived 
from 5 V using a voltage converter such as the Maxim 
max680.'' This is a low-power, CMOS, dc-to-dc converter 
that comes in an 8-pin, dual in-line package. This chip 
requires only four external capacitors to complete the 
circuit design and can operate up to 95% in voltage 
conversion efficiency. 

This approach increases flexibiUty because the 5-V sup- 
ply can be used in various appUcations without redesign. 
Other desired voltages can be derived as needed. 



''Reference to specific products does not imply endorsement by the 
U.S. Bureau of Mines. 



5-V do 

intrinsically safe 

power source 



5-V 



Board 1 



Local 
± 15-V 
regulator 



Board 2 



Local 
± 12-V 
regulator 



Board 3 



'egulotor 



Figure /.-Local regulation network. 



SPECIFICATIONS 



NOTE.-AIl speciflcations pertain to circuit operation at room temperature. 



Min 



Max Nominal 



5.5 
NAp 

8.5 
16.0 



Typical 



0.8 

2.7 

63 
1.5 

22 
5.5 

4.0 

4.0 

1.25 



5.0 
3.3 

7.9 
7.9 



Output: 

Adjustable voltage (Vj^, 7.9 V dc; load, 1.5 ohms; output voltage values as obtained 
by varying potentiometer R7) V dc . . 3.2 

Current (V^^, 7.9 V dc; V„„„ 5.0 V dc) : A . . NAp 

Input voltage, V dc: 

From battery pack 6.8 

From external voltage source 6.8 

Regulation, %: 

Line (V^^, 6.8 to 8.4 V dc; load, 1.5 ohms) 

Load (load current, 0.7 to 2.8 A; V^, 7.9) 

Miscellaneous: 

Efficiency (V^, 7.9; V„„„ 5.0; load, 1.5 ohms) % . . 

Battery hfe (V„^„ 5.5; load, 1.5 ohms; initial V^^, 8.44; final V^, 7.04) h . . 

Maximum power output W . . 

Weight (includes battery weight) lb . . 

Dimensions, in: 

Width 

Height 

Length 

NAp Not applicable. 



SUMMARY 

An intrinsically safe power supply with a regulated out- The power supply incorporates detection and protection 

put of 5 V at 4 A has been developed by the U.S. Bureau against excessive voltage and current, excessive circuit 

of Mines. Two rechargeable, sealed batteries are used as junction temperatures, and low battery conditions, 

the internal power source. External connections are pro- Complete information is supplied on circuit operation 

vided to monitor battery voltage, recharge the batteries, and calibration so that this power supply can easily be 

and to operate with an external power source connection. duplicated for industry use. 



APPENDIX A.-INTRINSIC SAFETY 



The Code of Federal Regulations^ defines intrinsic 
safety as "incapable of releasing enough electrical or 
thermal energy under normal or abnormal conditions to 



^U.S. Code of Federal Regulations. Title 30-Mineral Resources; 
Chapter I-Mine Safety and Health Administration, Department of 
Labor; Subchapter B-Testing, Evaluation, and Approval of Mining 
Products; Part 18-Electric Motor-Driven Mine Equipment and 
Accessories; Subpart A-General Provisions, Section 18.2, July 1, 1987. 



cause ignition of a flammable mixture of methane or 
natural gas and air of the most easily ignitable 
composition." 

The power supply has been tested by the Mine Safety 
and Health Administration (MSHA). Experimental Permit 
No. 596 has been issued to the Bureau for this device as it 
is used to power a specific system. Others wishing to use 
this power supply must have it certified by MSHA for use 
in their specific system. 



10 



APPENDIX B.-FABRICATION INFORMATION 

This appendix contains a list of parts needed to construct the rechargeable, intrinsically safe power supply described 
in this report. 



Item 

Battery: Bl, B2 

Capacitor: 

C2 

C3 

C4, C5, C6 

C7 

C8, C9 

CIO 

Diode: CRl, CR2, CR3 . . 

Fuse: Fl 

Linear regulator: 

Ul 

U2 

U3 

Rectifier: 

Dl, D2, D3 

D4 

Resistor: 

Rl 

R2 

R3 

R4 

R5 

R6 

R7 

R8, RIO, R12 

R9, Rll 

R13, R15 

R14, R16, R18 

R17 

R19 

R20 

R21 

R22 

R23 

R24 

R25 

R26 

Switch: SWl 

Transistor: 

Ql 

Q2 

SCR Silicon-controlled rectifier, 
WW Wire wound. 



Description 
CMF4V10 

OMl-nF, 50-V dc, monolithic . . . 

0.47-/iF, 35-V dc, tantalum 

l-/iF, 35-V dc, tantalum 

6.8-^F, 15-V dc, tantalum 

0.22-^F, 50-V dc, tantalum 

0.1-/iF, 50-V dc, monohthic .... 

1N5823A 

4-A, 250- V, type ABC, ceramic . 

UC3834N 16-pin IC 

LM308N 8-pin IC 

ICL7665CPA 8-pin I 

2N6400 SCR's TO-220 (case) . . . 
SA6.0A TransZorb 

10-ohm, WW, 10-W 

0.05-ohm, WW, fused, 2-W 

680-ohni, 1%, metal film 

15-ohm, 5%, WW, 1/2-W 

l-kohm, 1%, metal film 

1.2-kohm, 1%, metad film 

l-kohm (25T) #3299W ... 

8.25-kohm, 1%, metal film 

20-kohm (25T) #3299W 

10-kohm, 5% 

210-kohm, 1%, metal fihn 

132-kohm, 1%, meted film 

47.5-kohm, 1%, metal film 

52.1-kohin, 1%, metal film 

210-kohm, 1%, metal film 

3.92-kohm, 1%, metal film 

10-kohm, 5%, 1/4-W 

150-ohm, 5%, 1-W 

0.04-ohm, WW, 3-W, LPW3-2L . 

1.8-kohm, 5%, 1/2-W 

MTM-106D-RA PC-switch SPDT 

D45VH1 

IRF153 



Manufacturer 



Quantity 



Eagle Pitcher 

MaUory . . . . 

. . do 

. . do 

. . do 

. . do 

. . do 

Mot 

Little Fuse . 



Unitrode 

National Semiconductor 
Maxim 



Mot 

General Semiconductor 

Dale 

IRC 

Dale 

IRC-TRW 

Dale 

. . do 

Bourns 

. . do 

. . do 

IRC 

Dale 

do 

do 

do 

do 

do 

IRC 

IRC 

IRC 

IRC 

Alco 



GE 
GE 



1 
1 
3 
1 
2 
1 
3 
1 

1 
1 
1 

3 
1 

1 
1 
1 
1 
1 
1 
1 
3 
2 
2 
3 
1 
1 
1 
1 
1 
1 
1 
1 
1 
1 

1 

1 



11 



APPENDIX C.-BATTERY CHARGER 

The information presented in this appendix is sufficient for construction of the battery charger designed for the Bureau 
of Mines. This charger is not intrinsically safe. Do not attempt to use it in hazardous environments. Battery charging 
and replacement must be conducted in a safe, fresh air environment. The parts Ust and schematic diagram (fig. C-1) 
follow. 



Item 

Capacitor: 

Cll 

C12 

C13 

Diode: 

CR12 

CR13 

Diode bridge: Dl . . 
Linear regulator: U9 
Resistor: R9, RIO . . 
Transformer: Tl . . . 



Description 



Manufacturer 



Quantity 



2,100-/xF, 35-V dc 

0.1-/iF, 50-V dc 

l-/iF, 35-V dc 

31DQ03 IR 

80SQ035 IR 

Type KBPC602 

UA78GUIC 

RN65C, 39.2-kohm, 1% 
Type P-8642 



Mallory 

. . do 

. . do 

International Rectifier 

. . do 

General Instrument . . 

Fairchild 

Dale 

Stancor 



Current 
transformer, 
12.6 V, 6A 




CRI3 



+ Cll 

=^2,IOOyU.F 

35 V 



80S0035 
IR 



CI2 

0.1 ziF: 

50 V 



U9 



UA78GUIC 
Ground Sense 



q::CI3 
1/iF 
35 V 



R9 



• — 'vw- " — ^A/v 



39.2 kn 
17. 



CRI2 

-^ 

3ID003 
IR 



RIO 



39.2 kO 
l.7o 



J 2-4 

— > 



J2-2 



J2-3 



Chassis box, mechanical ground 



1 



D-^ 



Safety 
ground 



Figure C-1 .-Battery charging circuit schematic. 



us. GOVERNMENT PRINTING OFFICE: 611-012/00.085 



INT.BU.OF MINES,PGH.,PA 28923 



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